Gaseous discharge device



March 28, 1950 c. G. SMITH 2,502,236

GASEOUS DISCHARGE DEVICE Filed Sept. 12, 1945 Patented Mar. 28, 1950GASEOUS DISCHARGE DEVICE Charles G. Smith, Medford, Mass, assignor toRaytheon Manufacturing Company, Newton, Mass, a corporation of DelawareApplication September 12, 1945, Serial No. 615,847

v6 Claims.

This invention relates to gaseous electrical discharge devices, and moreparticularly to gaseous discharge devices of the hot cathode type.

The current carrying capacity of hot cathode gas filled tubes of thetype to which the invention relates is limited in practice by the factthat the oxide coated cathods disintegrate rapidly under positive ionbombardment when the ion velocity exceeds a critical value. Theionization potentials of some of the noble gases and of mercury vaporare sufficiently lower than the disintegration voltage to make itpossible to design hot cathode arc discharge tubes in which the cathodedoes not disintegrate, but this requires that the average anode currentbe kept below the value corresponding to the electron emission from thecathode.

It is among the objects of this invention to provide a hot cathodegaseous discharge device which will carry large currents at moderatelylow voltages and have long life although the gas or vapor in the tube isat a relatively low pressure.

To these ends the invention contemplates a construction in which thepositive ion space charge near the cathode is greatly increased overthat which is present in conventional constructions. This end isachieved by the provision of a magnetic field of high intensity in theregion immediately surrounding the cathode so that electrons flowing inthis region follow a much longer path than they would if the field werenot present. The voltage drop between the cathode and the surroundingionized gas therefore occurs in a very minute space. Voltage gradientsof one thousand Volts per centimeter or higher are thus obtained.

The above and other objects and features of the invention will be madefully apparent to those skilled in the art from a consideration of thefollowing detailed description taken in conjunction with theaccompanying drawing in which:

Fig. 1 is a sectional view with parts in side elevation of a dischargedevice embodying the invention together with the circuit diagramthereof; and

Fig. 2 is a sectional view of another embodiment of the invention.

Referrin to the drawing and first to Fig. 1 thereof, reference numeral 5indicates an envelope which, in the instance shown, is a tubular memberof non-magnetic material such as copper. The ends of the tubular member5 are closed by a pair of pole pieces 6 and I, each havin; axialpassages 8 and 9 extending therethrough. The passages 8 and 9 areenlarged at the outer ends thereof providing internally threadedportions H) and II to receive the externally threaded pipes I2 and 13which are hermetically sealed therein. The outer ends of the pipes l2and i3 are sealed by glass seals 14 and i5. Cathode lead-in conductorsl6 and I! are sealed through the glass seals M and I5 and extend throughthe axial passages 8 and 9 to provide lead-in conductors and supportsfor the cathode 18. The cathode I 8 is of the permanently energized typeand may be constructed, for example, of a coil of tungsten wiresurrounding a section of thorium. The pole pieces 6 and l are providedwith truncated conical portions projecting inwardly into the tubularmember 5 to points in close proximity with the oath- Ode 28 in order toprovide a strong magnetic field, which field is highly concentrated inthe annular space immediately surrounding the filament [8. A pair ofmain anodes i9 and 29 are positioned within the tube 5 in the annularspace adjacent the cathode 48,.and are supported by lead-in conductors2i and 22 which extend through pipes 25 and 26 sealed in openingsthrough the tube 5. The outer ends of the pipes 25 and 26 are sealed byglass seals 23 and 24 through which the lead-in conductors and supports2| and 22 are sealed. The anode lead-in conductors 2i and 22 areconnected to the end terminals of the secondary winding 2'! of a powersupply transformer 28 having a primary winding 29. A load 30 isconnected between a center tap 3! on the transformer 28 and a center tap32 On the secondary winding 33 of a transformer 34 having a primaryWinding 35. The outer ends of the secondary winding 33 of thetransformer 34 are connected to the lead-in conductors l6 and I! of thecathode I8 for supplying an energizing current to said cathode. Abattery 36 having its positive terminal connected through acurrent-limiting resistor 3'! to the tube 5 and its negative terminalconnected to one of the cathode lead-in conductors, in this instance I1,is provided in order to bias the pole pieces 6 and 1 positive relativeto the cathode 18. In the instance shown, a small quantity of mercury 38is provided in the envelope 5 sufficient when vaporized to provide a gasfilling within the envelope having a pressure of the order of 10 micronsmore or less. A filling of a permanent gas may be used in conjunctionwith the mercury, or such gas may be used alone where desired,

In the operation of the device described in the foregoing, when thecathode i8 is heated to a temperature at which there is appreciablethermionic emission, a small ionizing current fiows between the ends ofpole pieces 6 and and the cathode l8, due to the potential differenceapplied therebetween by the battery 36. The pole pieces 6 and I thusfunction as an auX- iliary starting electrode. When an alternatingvoltage is supplied to the anodes l9 and from the transformer 28, alarge current is drawn through the device between the cathode l8 and oneor the other of the anodes H1 and 20 depending on which ever of theseanodes is positive. Thus, on alternate half cycles, the current flowsfrom the left-hand side of the secondary winding 21 to the anode l9, andthence by way of the cathode It, the center tap 32 of the secondarywinding 33 of the transformer 34, the load 30, to the center tap 3| ofthe secondary winding 21. On the next succeeding alternation, thecurrent flows through the right hand side of the secondary winding 2i tothe anode 2i? and thence to the cathode l8 and through the load in thesame direction as when the voltage is applied to the anode Hi.

The magnetic field between the adjacent ends of the pole pieces 6 and 1has the effect of causing the electrons in the space immediatelysurrounding the cathode iii to follow much longer paths in fiowing fromthe cathode to the anode than they would follow if the field were notpresent. This results in a much greater ionization of the gas or vaporpresent in this region. An intense glow is produced in the regionimmediately surrounding the cathode even when the pressure is very low.The voltage drop between the cathode and the surrounding ionized gasoccurs in a very minute space. One thousand volts per centimeter andmuch higher gradients are possible. An atom of thorium attempting toleave the region will in general be ionized and immediately drawn backto the cathode. Thus the magnetic field so increases the degree ofionization and the voltage gradient that the loss of active cathodematerial is greatly reduced. Thus much higher currents may be drawnwithout destroying the cathode than are otherwise practical.Furthermore, auto-electronic emission becomes appreciable at the highercurrent densities and higher magnetic field strengths. 5

Thus, at moderate intensities of the magnetic field, the cathode isoperative in regions of lower pressure than normally expedient. Wherethe field is of high intensity, the cathode is operative underconditions of greater emissivity than normally practical.

In operating with a very intense magnetic field I prefer to use a baretungsten or tantalum cathode which can be operated at higher temperaturethan is normally practical and the voltage gradient at the emittingsurface makes possible additional thermionic emission, with a resultingdischarge giving an apparently unlimited cathode emission or causing anapproach to such conditions.

The magnetic field may be derived from a permanent magnet such as 39connecting the outer ends of the two pole pieces 6 and 1. Obviously,instead of a permanent magnet, an electromagnet may be utilized. It willbe understood that where the device is to be utilized as a half waverectifier rather than a full wave rectifier, only one main anode l9 or20 and its corresponding connections need be provided.

In some instances I prefer to dispose the magnet within the evacuatedspace of the envelope. In Fig. 2 a permanent magnet 4| is disposedwithin the envelope 42 being positioned by support 43 in a press 44 of areentrant stem 45. The lead-in conductors 46 and 41 sealed through thepress 44, supply the cathode 48 with energizing current. In order tosupport the cathode 48 in a position coaxial with the magnetic fieldprovided by the magnet 4|, the pole pieces of said magnet may beprovided with longitudinal bores 49 and 50 through which the lead-inconductors 46 and 41 extend to support the cathode 48. In order tomaintain the lead-in conductors 46 and 41 in spaced relation to theinterior walls of the bores 49 and 5|], one or more glass beads 5|5| orequivalent spacing devices may be provided in each of the bores 49 and50. In order to supply a positive potential to the magnet 4! relative tothe cathode 48, a lead-in conductor 52 is provided, which conductor issealed within the press 44 and connected to one of the supports 43 forthe magnet 4|. Anodes 53 and 54 are positioned in the envelope 42 in thespace outside of the field of the magnet 4|. A small quantity of mercury55 provides an ionizable medium of relatively low pressure within theenvelope 42 when the tube is in normal operation. As in the constructionpreviously described, other ionizable mediums may be utilized.

It will be understood that the external circuit of the form of thedevice shown in Fig. 2 may be identical with the circuit shown in Fig.1, and when so connected the operation of the device as a rectifier willbe the same as the operation previously described in conjunction withFig. 1. It will be understood that instead of functioning as arectifier, either tube may be utilized as an oscillator, or for otherpurposes.

While there have been herein described certain preferred embodiments ofthe invention, other embodiments within the scope of the appended claimswill be apparent to those skilled in the art from a consideration of theembodiments shown and the teachings hereof. Accordingly, a broadinterpretation of the appended claims commensurate with the scope of theinvention within the art is desired.

What is claimed is:

1. A gaseous conduction device comprising an envelope'containing anionizable medium, a cathode of the heated type having an electronemissive surface in said envelope, a main anode spaced from said cathodeand providing an electron path I therebetween, and means, for returningto said cathode surface electron emissive material thrown oif therefrom,comprising a magnetic field concentrated in the space immediatelysurrounding said cathode surface, said field extending transversely tothe normal direction of electron fiow between said cathode and saidanode.

2. A gaseous conduction device, comprising an envelope containing anionizable medium, a pair of pole pieces mounted within said envelope andseparated by a gap, a cathode of the heated type positioned in said gap,and means for returning electron emissive material thrown off from saidcathode surface to said cathode surface comprising means forestablishing a magnetic field between said pole pieces across said gap,and a main anode in said envelope spaced from said cathode and from saidpole pieces and providing an electron path between said cathode and saidanode, said field having its greatest intensity in the space immediatelysurrounding said cathode and extending transversely to the normaldirection of electron flow between said cathode and said anode.

3. A gaseous conduction device comprising an velope containing anionizable medium at a pressure of the order of ten microns, a pair ofpole pieces mounted within said envelope and separated by a gap, acathode of the heated type positioned in said gap, and means for forcingmaterial thrown off from said cathode surface back to said cathodesurface, comprising means for establishing a magnetic field between saidpole pieces across said gap, and a main anode in said envelope spacedfrom said cathode and from said pole pieces and providing an unimpededelectron path between said cathode and said anode, said field having itsgreatest intensity in the space immediately surrounding said cathode andextending transversely to the normal direction of electron flow betweensaid cathode and said anode, said pole pieces cooperating with saidcathode to maintain an auxiliary discharge in the normal operation ofsaid device.

4. An electron discharge device comprising an envelope containing acathode of the heated type having a surface comprising electron emissivematerial, an anode spaced'from said cathode, and

means, for returning atoms of material vaporized from said cathode tosaid cathode surface, comprising means for applying a magnetic fieldacross the space surrounding said cathode in a direction transverse tothe direction of normal electron fiow, and an ionizable mediumsurrounding said cathode.

5. An electron discharge device comprising an envelope containing acathode of the heated type having an electron emissive surface, an anodespaced from said cathode, means for applying a potential between saidanode and said cathode, and means, for returning to said cathodematerial vaporized from said cathode, comprising means for applying amagnetic field across the space surrounding said cathode in a directiontransverse to the direction of normal electron flow,

and an ionizable medium surrounding said cath ode, for increasing thepotential gradient sure rounding said cathode, whereby electrons emittedfrom said cathode are accelerated at an increased rate, and ionizedparticles of vaporized material from the cathode are forced back to saidcathode.

6. An electron discharge device comprising an envelope containing acathode of the heated type and an anode spaced therefrom, means forproducing the ionization of material vaporized from said cathodecomprising means for applying a magnetic field across the spacesurrounding said cathode in a direction transverse to the direction ofnormal electron flow, whereby said electrons are retained in the areasurrounding the cathode for an increased length of time and theprobability of their striking material emitted from the cathode andionizing same is greatly increased, means for increasing theelectrostatic force between material vaporized from said cathode andionized by said electrons comprising an ionizable material surroundingsaid cathode for increasing the potential gradient in the areasurrounding said cathode.

CHARLES G. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,558,120 Simpson Oct. 20, 19252,039,100 McArthur Apr. 28, 1936 2,135,006 Jurriaanse Nov. 1, 19382,182,736 Penning Dec. 6, 1939 2,238,272 Linder Apr. 15, 1941 FOREIGNPATENTS Number Country Date 147,856 Great Britain Jan. 9, 1922 527,131France July 18, 1921

